October 2020, ScientificAmerican.com 53THE HUNGER WINTER
DeCaDes Of Careful ObserVaTIOn and analysis have
gone into uncovering the manifold ways in which the
fetal environment affects the future health and pros-
pects of a child, and much remains mysterious. It
would be unethical to run experiments to measure
the toll on a fetus of, say, malnutrition or pollution.
But we can look for so-called natural experiments—the
(sometimes horrific) events that cause variations in
these factors in ways that mimic an actual experiment.
The late epidemiologist David Barker argued in the
1980s that poor nutrition during pregnancy could
“program” babies in the womb to develop future ail-
ments such as obesity, heart disease and diabetes. Ini-
tial evidence for such ideas came from studies of the
Dutch “Hunger Winter.” In October 1944 Nazi occu-
piers cut off food supplies to the Netherlands, and by
April 1945 mass starvation had set in. Decades later
military, medical and employment records showed
that adult men whose mothers were exposed to the
famine while pregnant with them were twice as like-
ly to be obese as other men and were more likely to
have schizophrenia, diabetes or heart disease.
Anyone born in the Netherlands during the famine
is part of a cohort that can be followed over time
through a variety of records. Nowadays many research-
ers, including me, look for natural experiments to
delineate such cohorts and thereby tease out the long-
term impacts of various harms experienced in utero.
We also rely heavily on the most widely available mea-
sure of newborn health: birth weight. A baby may have
“low” birth weight, defined as less than 2,500 grams
(about 5.5 pounds), or “very low” birth weight of less
than 1,500 grams (3.3 pounds). The lower the birth
weight, the higher the risk of infant death. We have
made enormous progress in saving premature babies,
but low-birth-weight children are still at much higher
risk for complications such as brain bleeds and respi-
ratory problems that can lead to long-term disability.
In recent years computer analysis of large-scale elec-
tronic records has made it possible to connect infant
health, as measured by birth weight, to long-term out-
comes not just for cohorts but also for individuals. Stud-
ies of twins or siblings, who have similar genetic and
social inheritance, show that those with lower birth
weight are more likely to have asthma or attention def-
icit hyperactivity disorder (ADHD) when they get older.
Several studies also show that lower-birth-weight twins
or siblings have worse scores on standardized tests. As
adults, they are more likely to have lower wages, to
reside in lower-income areas or to be on disability-assis-
tance programs. In combination, cohort and sibling
studies demonstrate that low birth weight is predictive
of several adverse health outcomes later in life, includ-
ing increased probabilities of asthma, heart disease, dia-
betes, obesity and some mental health conditions.
Birth weight does not capture all aspects of a child’s
health: a fetus gains most of its weight in the third tri-
mester, for example, but many studies find that shocks
in the first trimester are particularly harmful. I none-
theless use the measure in my studies because it is
important and commonly available, having been record-
ed for tens of millions of babies for decades.
Significantly, low birth weight is much more com-
mon among infants born to poor and minority mothers.
In 2016 13.5 percent of African-American mothers had
low-birth-weight babies, compared with 7.0 percent of
non-Hispanic whites and 7.3 percent of Hispanic moth-
ers. Among those with college educations, 9.6 percentof Black mothers had low-birth-weight babies, compared
with 3.7 percent of non-Hispanic white mothers. These
inequalities in health at birth reflect large differences in
exposure to several factors that affect fetal health.THE POVERTY CONNECTION
as alreaDy nOTeD, the quality of a mother’s nutrition
substantially influences the health of her babies. In 1962
geneticist James V. Neel hypothesized that a so-called
thrifty gene had programmed humankind’s hunter-
gatherer ancestors to hold on to every calorie they
could get and that in modern times, that tendency,
combined with an abundance of high-calorie foods,
led to obesity and diabetes. Recent studies on labo-
ratory animals indicate, however, that the link be -
tween starvation and disease is not genetic in origin
but epigenetic, altering how certain genes are “ex -
pressed” as proteins. Prolonged calorie deprivation
in a pregnant mouse, for example, prompts changes
in gene expression in her offspring that predispose
them to diabetes. What is more, the effect may be
transmitted through generations.
Outright starvation is now rare in developed coun-
tries, but poorer mothers in the U.S. often lack a diet
rich in fruits and vegetables, which contain essential
micronutrients. Deficiencies in folate intake during
pregnancy are linked to neural tube defects in children,
for example.
At present, one of the leading causes of low birth
weight in the U.S. is smoking during pregnancy. In
the 1950s pregnant women were told that smoking
was safe for their babies. Roughly half of all new
mothers in 1960 reported smoking while pregnant.
To day, thanks to public education campaigns, indoor-
smoking bans and higher cigarette taxes, only 7.2 per-
cent of pregnant women say that they smoke. And
55 percent of women who smoked in the three months
before they got pregnant quit for at least the duration
of their pregnancy.
Possibly because going to college places women in
a milieu where smoking is strongly discouraged, moth-Poor nutrition during pregnancy
can “program” babies in the womb
to develop future ailments.
© 2020 Scientific American